In a valve gated injection molding apparatus, a valve pin is slidable through a nozzle channel of a nozzle to selectively close a mold gate and restrict melt flow into a mold cavity. The valve pin slides through a valve pin bushing, which has a bore machined to a high tolerance to fit the valve pin to inhibit leakage of molten material from the nozzle melt channel and provide alignment of the valve pin with the mold gate.
During the injection process, some plastic materials may release gases especially at high temperatures. This gas may escape from the injection molding apparatus through the valve pin receiving bore of the valve pin bushing. Upon contacting colder surfaces within the valve pin bushing, the gas condenses into a liquid and in time, may degrade and harden. The hardened material may inhibit or restrict movement of the valve pin and require the apparatus to be shut down for cleaning and/or repair.